Hydrodynamic Simulations of Oxygen–Neon Classical Novae as Galactic ⁷Li Producers and Potential Accretion-induced Collapse Progenitors

We report on studies of classical nova (CN) explosions where we follow the evolution of thermonuclear runaways (TNRs) on oxygen–neon (ONe) white dwarfs (WDs). Using NOVA, a 1D hydrodynamic computer code, we accrete solar matter until the TNR is ongoing and then switch to a mixed composition. This approach is guided by the results of multidimensional studies of TNRs in WDs, which find that sufficient mixing with WD core material occurs after the TNR is well underway, and levels of enrichment of the CNONeMg elements are reached that agree with observations of CN ejecta abundances. Because the amount of accreted material is inversely proportional to the oxygen abundance, by first accreting solar matter, the amount of accreted material is larger than in those simulations with an initially enriched composition. We vary the mass of the WD (from 0.6 M_⊙ to 1.35 M_⊙) and the composition of the mixed materials. Our results show large enrichments of ⁷Be in the ejected gases, implying that ONe CNe and CO CNe may be responsible for a significant fraction (∼100 M_⊙) of the Galactic 7Li (∼1000 M_⊙). The production of ²²Na and ²⁶Al in CN explosions and the γ-ray emission predicted by our simulations are discussed. The WDs in all our simulations eject less material than they accrete and we predict that the WD is growing in mass as a consequence of the CN outburst. ONe CNe, therefore, may be an important channel for accretion-induced collapse events.